Selenium is a possible cancer preventive agent, and is being considered for use in intervention trials. A study in collaboration with the Cancer Prevention Studies Branch (Z01 CN 00101 CPSB) is in progress which will provide information on the pharmacokinetics of selenium in its prototype forms -- sodium selenite (inorganic form) and selenoethionine (organic form). This information is unavailable for these agents in the dose currently considered optimal, and is necessary to the determination of time and manner of administration. Parameters such as percent absorption, maximum concentration, time to maximum concentration and mean residence time will be estimated for a single dose and compared in fasting and non-tasting subject. In order to interpret the study data more fully, development of integrated kinetic models, one for selenite and one for selenoethionine, will be attempted. Such models are useful in making inferences about drug metabolism and about the distribution of the drug in various body pools. A model for selenite is under development. It is anticipated that the models will result in population estimates of mean residence times and rates of exchange between body pools. The Biometry Branch, in cooperation with the Cancer Prevention Studies Branch, is functioning as a data collection center, had primary responsibility for the study design, and has primary responsibility for data analysis.